This is taken from an article at bethinking.org.
If a document contains features which are embarrassing or counterproductive to the purpose for which it was written, then it has a high probability of being historical [cf. Gottschalk, Understanding History, pp. 156-65]. There would be no sufficient reason other than their facticity for including such features.
Instances of this occur frequently in the Gospels. Jesus' denial of being good is an example [see A. R. C. Leaney, ‘Historicity in the Gospels’, in Vindications, ed. Anthony Hanson (New York: Morehouse-Barlow, 1966), p.120. To this may be added Mark 13:32; 15:34. Jesus’ attitudes toward legalism, fasting, divorce, sinners, and women were radical and somewhat embarrassing. Several features of Jesus' character were stumbling blocks, including his displays of anger, his baptism, his death on a cross, and the fact that he was a carpenter from Nazareth. To this could be added the opposition to Jesus from his family. [40] Also, the portrayal of the disciples is often embarrassing (e.g., when they are in unbelief, show cowardice, or have difficulty with Jesus' teaching). The request of the sons of Zebedee is surely authentic, as is Matthew 23:8, 10, which would seem to condemn the churches' own practice of having official teachers.
Mark 13:32
No One Knows That Day or Hour
32 “But concerning that day or that hour, no one knows, not even the angels in heaven, nor the Son, but only the Father. (ESV)
Mark 15:34
34 And at the ninth hour Jesus cried with a loud voice, “Eloi, Eloi, lema sabachthani?” which means, “My God, my God, why have you forsaken me?” (ESV)
